There has conventionally been known a technique of establishing communication between an apparatus such as an electric meter and an external apparatus such as a remote server through a TCP (Transmission Control Protocol)/IP (Internet Protocol) gateway.
In this technique, the electric meter transmits measurement data measured by itself to the TCP/IP gateway as a non-IP packet by using Layer 2 frame, and the TCP/IP gateway transmits the measurement data received from the electric meter to the remote server by using HTTP (Hyper Text Transfer Protocol) over TCP/IP.
This configuration can simplify the electric meter in the communication between the electric meter and the remote server.
However, the above-mentioned conventional technique entails a security problem, which is such that an invalid apparatus can undesirably communicate with the external apparatus.